1. Field of the Invention
The invention pertains to a flat display apparatus, and more particularly to a method and apparatus that inspects for shorts and open circuits in the signal wires of a flat display apparatus by using a magnetic sensor.
2. Description of the Related Art
The importance of a display apparatus as a visual information transfer medium has recently enlarged. Widely used conventional cathode ray tubes have undesirable weight and large volume. There has therefore been developed various types of flat display apparatuses capable of overcoming the disadvantages of cathode ray tubes.
Examples of currently commercially available flat panel displays include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electroluminescence display (EL).
The liquid crystal display device readily adapts for miniaturization and has the additional advantage of improved productivity. Thus, LCDs are fast replacing the cathode ray tube in many applications.
Specifically, an active matrix type liquid crystal display apparatus that drives a liquid crystal cell by using a thin film transistor (hereinafter referred to as “TFT”) has an advantage of excellent picture quality combined with low power consumption. This technology has rapidly developed to large volume production of high definition displays due to recent research and the application of productivity technology.
The process for fabricating an active matrix type liquid crystal display apparatus is divided into substrate cleaning, substrate patterning, alignment forming/rubbing, substrate assembling/liquid crystal material injecting, mounting, inspecting, repairing, etc.
Impurities on a substrate surface of the liquid crystal display during the substrate cleaning process are removed by a detergent.
The substrate patterning process includes patterning of an upper substrate, i.e., a color filter substrate and a patterning of a lower substrate of, for example, a TFT array substrate. There are formed a color filter, a common electrode, a black matrix, etc. on the upper substrate. There are also formed signal wires such as a data line and a gate line on the lower substrate. The TFT is formed at an intersection of the data line and the gate line, and a pixel electrode is formed in a pixel region between the gate line and the data line connected to a source electrode of the TFT.
An alignment film is applied to each of the upper substrate and the lower substrate during the alignment film forming/rubbing process, and the alignment film is rubbed by a rubbing material.
During the substrate assembling/the liquid crystal injection process, both of the upper substrate and the lower substrate are bonded together with a sealant, and the liquid crystal material and a spacer are injected through a liquid crystal injection hole. Then, the liquid crystal injection hole is sealed.
The mounting process of the liquid crystal panel uses a tape carrier package (hereinafter referred to as “TCP”) having integrated circuits mounted thereon, such as a gate drive integrated circuit and a data drive integrated circuit connected to a pad part on the substrate. Such integrated driving circuits may be directly mounted on the substrate by using a chip on glass (herein after referred to as “COG”) method other than TAB (Tape Automated Bonding) using the TCP described above.
The inspecting process includes a first electrical inspection performed after a variety of signal wires and the pixel electrode are formed. An electrical inspection and a visual inspection are performed after the substrate assembly/liquid crystal injection process. Specifically, the electrical inspection of the signal wire and the pixel electrode of the lower substrate, followed by the substrate assembling, may reduce the defect ratio and the amount of waste matter. Also, a bad substrate may be capable of repair at an early stage, and thus its importance gradually increases.
The repairing process performs a restoration of a repairable substrate that is determined during the inspecting process. However, in the inspecting process, bad substrates that are beyond repair are discarded.
The electrical inspection being performed before substrate assembly frequently employs a method using an apparatus shown in FIG. 1.
Referring to FIG. 1, the electrical inspection process is performed as follows: a separate modulator 10 has a designated gap over a test substrate 11. Applying a test voltage (Vtest) to the modulator, while maintaining the gap, and detecting light reflected from the modulator 10 determines any electrical defects in the signal wires 17 and 18.
In the modulator 10, a polymer-dispersed liquid crystal (hereinafter referred to as “PDLC”) is put between an upper transparent substrate 12, having a common electrode 13, and the lower transparent substrate 15. In the modulator 10, a reflection sheet 16 is placed toward a rear surface of the lower transparent substrate 15. The modulator 10 has an air nozzle and a vacuum nozzle for an auto-gapping to maintain the designated interval from the detected substrate 11.
Above the modulator 10, a lens 21 light-gathers the light from a light source (not shown) into the modulator 10, and the lens 21 additionally transmits the light 22 reflected from the modulator 10.
The substrate 11 to be tested is the lower substrate on which is found the TFT, the signal wires 17 and 18 and the pixel electrode 20, which form the active matrix type liquid crystal display apparatus. The test substrate 11 shown in FIG. 1 is an equivalent circuit showing a portion of the total TFT array.
The test substrate 11 is loaded below the modulator 10, and then the modulator descends and performs the auto-gapping. Then, the electrical inspection begins. While the gap between the modulator 10 and the test substrate 11 is maintained at a pre-set effective gap, the light radiated from the light source (not shown) is light-gathered in the modulator 10 by the light-gathering lens, and the test voltage (Vtest) is simultaneously applied to the common electrode 13. The test data is applied from a driving circuit to the data wire 17, and a test scan signal is applied to the gate wire 18. Then, an effective electric field is applied to the PDLC 14 between the common electrode 13 of the modulator 10 and the pixel electrode 20 to be tested.
When the electric field is not applied, the PDLC 14 causes the light to scatter. When the effective electric field (E) is applied, the liquid crystal orients according to the direction of the effective electric field (E) and causes the light to transmit. Accordingly, in the electrical inspection process, when the voltage is normally applied to the pixel electrode 20, the corresponding liquid crystal layer of the PDLC 14 causes the light 22 to transmit. When the voltage is not applied to the pixel electrode 20, the liquid crystal layer of the PDLC 14 causes the light to scatter in that part.
While the light 22 transmitting to the liquid crystal layer of the PDLC 14 is reflected on the reflection sheet 16 and is reverse directed to a light path, the light 22 scattered in the liquid crystal layer of the PDLC 14 nearly vanishes and is not nearly incident to the reflection sheet 16. The light reflected in the modulator 10 is received to a charge-coupled device (CCD) (not shown) via the lens 21 and then is converted to an electrical signal. The received signal converted electrically is then transferred to a display apparatus (not shown) via a signal processing circuit. A testing inspector monitors an image or data displayed in the display apparatus to determine whether it is bad or not. The testing inspector secondarily performs a close inspection of doubtful points the signal (data and gate) wires 17 and 18.
The modulator 10 also has an advantage of exactness and reliability capable of inspecting for defects pixel by pixel, but it has a defect of high price. Further, since the inspection region is narrow as compared with total substrate 11 area, the modulator 10 repeats the process of transferring by a designated length in a vertical or a horizontal direction, and then stopping temporarily for auto-gapping. There is thus the disadvantage that the inspection time becomes long. That is, as shown in FIG. 2, the modulator 10 scans the obliquely lined part smaller than the substrate 11 at the incipient location, and then moves and stops at an adjacent sub-block, and then performs auto-gapping and scanning. The stepping, the auto-gapping and the moving are repeated in the horizontal direction and in the vertical directions. For example, in order to entirely scan a substrate having a size of 14.1 inches (36 cm), the modulator repeats fourteen times the step of auto-gapping and then moving. Accordingly, the inspection method of using the modulator 10 has a disadvantageously long inspection time.